Respiratory oxygen consumption measuring device and method

ABSTRACT

A portable apparatus for calculating respiratory oxygen consumption comprising a housing having a fluid inlet, a flow sensor, mounted within the housing, an oxygen sensor and means for calculating the respiratory oxygen consumption using data obtained from the oxygen sensor and the flow sensor. The invention also relates to a method of calculating respiratory oxygen consumption.

FIELD OF THE INVENTION

The present invention relates to methods of and apparatus forcalculation of respiratory oxygen consumption, in particular, althoughnot exclusively, to indirect calorimeters and methods of using the same.

BACKGROUND OF THE INVENTION

Techniques of calorimetry are used to study the energy of metabolism inhumans and animals. Calorimetry is used, for example, for diagnosis ofmetabolic disorders and for calculating nutritional requirements of asubject. Calorimetric measurements can be made directly as a measure ofheat loss of a subject. Alternatively, indirect measurements can be madeof a chemical by-product of metabolism.

A useful measure for nutritionists and sports scientists when assessingthe health and fitness of a subject is the volume of oxygen consumed atrest and during or after physical exertion.

Indirect calorimetry often involves measuring the amount of carbondioxide exhaled by a subject, which can in turn be used to calculate theoxygen consumption of the subject.

U.S. Pat. No. 5,178,155 discloses an indirect calorimeter that comprisesa carbon dioxide scrubber arranged to remove carbon dioxide from theexhaled gas and in some embodiments from the inhaled gas also. Thevolume of oxygen consumed can be calculated from the amount of carbondioxide removed from the exhaled gas by the scrubber. The calorimeter ofU.S. Pat. No. 5,178,155 also comprises two flow meters, the first beingarranged to monitor the inhaled gas flow and the exhaled gas flow afterremoval of the carbon dioxide and the second being arranged to monitorthe exhaled gas flow before removal of the carbon dioxide.

International patent application number PCT/US99/17553 discloses amethod and apparatus for analysing respiratory gases to determine oxygenconsumption for indirect calorimetry purposes as well as carbon dioxideproduction by measuring the mass and volume flow rate of inhaled andexhaled gas. The flow measurements are made using known ultrasonic pulsetransit time techniques. The gas density may be determined usingacoustic impedance, speed of sound or temperature related techniques.The method involves calculating the oxygen content in the inhaled andexhaled gas. In one embodiment of PCT/US99/17553 measurements are madeon the exhaled gas flow only. In this case, it is necessary to be awareof the oxygen content of the inhaled gas.

International patent application number PCT/US98/05297 discloses acalorimeter comprising a flow meter and a capnometer to compute thedifference between the inhaled gas volume and the volume of the exhaledgas less the carbon dioxide volume. The capnometer measures theconcentration of exhaled carbon dioxide. The amount of carbon dioxide inthe exhaled gas can then be subtracted from the total volume of exhaledgas to obtain a value for the volume of exhaled gas excluding carbondioxide. A bidirectional flow mater is also used to measure the flowrate of the inhaled and exhaled gas.

International patent application number PCT/US91/04587 discloses acalorimeter comprising means to condition inhaled gas to a temperatureand water vapour comparable with that of the exhaled gas, then thevolume of inhaled gas is measured. Carbon dioxide is removed from theexhaled gas by passing the exhaled gas through a carbon dioxide scrubberand then its volume is measured. A single flow meter may be used tomeasure the volume of both the inhaled and exhaled gas.

All of the indirect calorimeters described above are complicated tomanufacture and use. It is an aim of preferred embodiments of thepresent invention to provide an alternative method and apparatus forcalculating respiratory oxygen consumption and to provide an alternativeindirect calorimeter and method of using the same.

SUMMARY OF THE INVENTION

The present invention provides a portable apparatus for calculatingrespiratory oxygen consumption comprising a housing having a fluidinlet, a flow sensor mounted within the housing, an oxygen sensor andmeans for calculating respiratory oxygen consumption using data obtainedfrom the oxygen sensor and the flow sensor.

By “portable apparatus” we mean an apparatus that is hand portable suchthat it can be carried and used by an individual and can be hand held inuse.

Suitably, the apparatus is an indirect calorimeter.

Suitably, the housing is generally tubular. The tubular housing may haveany suitable cross-sectional shape.

Preferably the flow sensor comprises a movable member, movable by airpressure effected thereupon, and a movement sensor associated with themovable member.

Suitably, movement of the movable member within the housing is effectedby passing a fluid into the housing through the fluid inlet. Suitably,the fluid is a gas. Suitably, the gas is exhaled breath.

The movable member may be a rotatable member, such as a rotor or paddlewheel, for example.

Alternatively the movable member may be a plunger, slidably mounted withthe housing.

Suitably, the plunger is arranged to move slidably along the length ofthe tubular housing.

Suitably, there is a substantially fluid tight contact between theperiphery of the plunger and the interior surface of the housing.Suitably, the cross-sectional shape of the plunger corresponds with thecross-sectional shape of the interior of the tubular housing.

Suitably the oxygen sensor is mounted to the housing, preferably withinthe housing.

The oxygen sensor may comprise any suitable oxygen sensor. An exampleofa suitable oxygen sensor is an MOX-1™ sensor available from CityTechnology Limited of Portsmouth, England.

Suitably, when the movable member comprises a plunger the oxygen sensoris attached to an end of the plunger. Preferably, the oxygen sensor isattached to an end of the plunger that is nearest the fluid inlet.

The oxygen sensor may be either directly or indirectly attached to thesurface of the movable member. Alternatively, or in addition the oxygensensor may be embedded in the movable member.

Alternatively, or in addition the oxygen sensor may be separate from themovable member.

The movement sensor is, suitably, arranged to measure the speed ofmovement of the movable member during use of the apparatus according tothe invention.

Any suitable movement sensor may be used. For example, the movementsensor may comprise one or more sensor switches. Suitable sensorswitches include a slotted opto switch number 304-560 available from RSComponents Limited of Corby, England.

Suitably, the movement sensor is attached, either directly orindirectly, to the movable member. Preferably, a movement sensor isembedded in the movable member.

The movement sensor may comprise a first switch located on the movablemember and a second switch located on the housing.

If the movable member is a rotor or paddle wheel, there may be pluralityof first switches, each mounted on a separate blade of the motor, and asecond switch located on the housing.

Suitably, the apparatus for calculating respiratory oxygen consumptionis arranged such that the movable member moves only a pre-set distancewithin the housing during use. Suitably, the movable member movesbetween a start position and an end position.

The apparatus for calculating respiratory oxygen consumption may furthercomprise a fluid outlet. Suitably, when the movable member is a plungerthe fluid outlet is located adjacent the end position of the plunger.Suitably, the fluid outlet is positioned such that excess exhaled breathpasses out of the housing through the fluid outlet once the plungerreaches the end position and does not cause continued movement of theplunger within the housing.

The apparatus may further comprise a collection chamber. The collectionchamber may be in direct or indirect fluid flow communication with thefluid outlet. The collection chamber may comprise any suitable device,for example a bag or box. Suitably, the oxygen sensor is located in thecollection chamber. Suitably the collection chamber forms part of thehousing of the apparatus and is therefore integral with the housing.

If the movement sensor comprises a first switch located on the movablemember and a second switch located in the housing, the second switch issuitably located adjacent the fluid outlet. Suitably, the second switchis located downstream of the fluid outlet relative to the fluid inlet.When the movable member is a plunger, suitably the second switch islocated at the end position of the plunger.

When the movable member is a plunger the apparatus in accordance withthe present invention may comprise means to return the plunger to thestart position. Suitably, the apparatus comprises means to return theplunger to the start position after calculation of the respiratoryoxygen consumption has been made. Any suitable means of returning theplunger to the start position may be used, for example a spring.

The fluid inlet is suitably arranged to allow ingress of exhaled breathfrom a subject using the apparatus into the apparatus. The fluid inletmay be provided by the end of the housing.

Suitably, apparatus in accordance with the present invention comprises amouthpiece associated with the fluid inlet. The fluid inlet may beprovided by the mouthpiece. Alternatively, the fluid inlet may beseparate from the mouthpiece. If the mouthpiece is separate from thefluid inlet, the mouthpiece is suitably directly connected to the fluidinlet.

The apparatus according to the present invention may comprise an openingin the housing. Suitably, the opening provides for external fluid to beinhaled through the apparatus by the subject using the apparatus. Theopening may be sealed by a one way valve, which valve allows fluid to beinhaled through the opening but prevents exhaled fluid from passingthrough the opening. Suitably, substantially no movement of the movablemember occurs when fluid is inhaled through the opening by the subject.If the movable member is a plunger, suitably the opening is locatedbetween the fluid inlet and the end of the plunger when the plunger islocated in the start position.

The apparatus in accordance with the present invention may comprise anysuitable means for calculating the respiratory oxygen consumption. Forexample, the apparatus may comprise a computer or other electronicdevice for calculating the respiratory oxygen consumption. The means forcalculating the respiratory oxygen consumption may be mounted on thehousing of the apparatus or detachably connected to the housing.

The present invention further provides a method of calculatingrespiratory oxygen consumption comprising the following steps:

-   -   (a) passing an exhaled breath into a housing;    -   (b) measuring the fraction of oxygen in the exhaled breath using        an oxygen sensor;    -   (c) measuring the time taken to exhale the breath using a flow        sensor mounted within the housing; and    -   (d) calculating the oxygen consumption using the data obtained        in steps b and c.

Suitably, step (a) comprises passing an exhaled breath of known valueinto the housing.

Suitably the flow sensor comprises a movable member associated with amovement sensor and step (a) comprises passing an exhaled breath into ahousing to cause movement of a movable member.

Suitably, the method of calculating respiratory oxygen consumption is amethod of indirect calorimetry.

The method of the present invention may be carried out using theportable apparatus of the present invention.

When the apparatus comprises a movable member, suitably the volume ofthe exhaled breath is calculated by measuring the extent of movement ofthe movable member.

When the movable member is a plunger, suitably the volume of the exhaledbreath is calculated by measuring the distance moved by the plunger.

The range of movement of the movable member within the housing may berestricted to a pre-set distance.

Alternatively, movement of the movable member is not restricted but themovement sensor and the oxygen sensor are arranged to take measurementsonly during movement of the movable member over a restricted movementrange.

In both cases, measurements are made using the oxygen sensor and themovement sensor only for the duration of exhalation of a known volume ofbreath.

The method may be repeated one or more times to obtain an averagecalculation of oxygen consumption. If the method is repeated one or moretimes, the results are suitably integrated to provide an average figure.

The apparatus of the present invention and the method of the presentinvention may use the following formula to calculate the respiratoryoxygen consumption per breath exhaled:VO ₂ =K×(F _(i) O ₂ −F _(e) O ₂)×V×(30/t)×C  Formula IWhere,

VO₂ is the respiratory oxygen consumption of the subject

F_(i)O₂ is the fraction of inhaled oxygen

F_(e)O₂ is the fraction of exhaled oxygen

V is the volume of the exhaled breath over which the measurements aretaken

t is the time taken to exhale the known volume of breath

C is the constant calorific value for oxygen (approximately 5 kcal).

K is a constant allowing for calibration.

The fraction of inhaled oxygen can be calculated from the gas inhaled bythe subject. For instance, if the subject inhaled atmospheric air, thefraction of inhaled oxygen can either be assumed to be the standardvalue of 20.94%, or the actual fraction of oxygen in the atmospheric aircan be measured using any known technique.

The fraction of exhaled oxygen is measured using the oxygen sensor.

The volume of the exhaled breath can be measured by any suitable method.Suitably, when the apparatus comprises a movable member, the movablemember moves a known extent within the housing and this distance is usedto measure the volume of the exhaled breath in respect of whichmeasurements are taken. If the oxygen sensor is attached to the surfaceof the movable member the volume calculation must take into account thevolume reduction caused by the presence of the oxygen sensor.

Suitably, in use, the movable member is arranged in the housing at astart position at which a first switch of a movement sensor is spacedapart from a second switch of the movement sensor. When exhaled breathpasses into the housing the movable member suitably moves towards thesecond switch. Preferably, the movement sensor takes a measurementduring movement of the first sensor from its start position until thefirst sensor reaches the position of the second sensor. In this way, themovement sensor takes measurements only for the duration of exhalationof a breath.

During exhalation of the breath the oxygen sensor measures the fractionof molecular oxygen in the exhaled breath.

The data obtained from the oxygen sensor and the flow sensor may then beused to calculate the oxygen consumption of the subject per breath usingFormula I.

If the apparatus in accordance with the present invention compriseselectronic means to calculate the oxygen consumption, the oxygen sensorand the flow sensor suitably transmit the data obtained directly to theelectronic calculation means by means of electronic signals.

Advantageously, the method and apparatus of the present invention can beused to provide information on the oxygen consumption of a subject, forexample a human or an animal.

The apparatus and method of the present invention are advantageouslyeasy to use. Furthermore, the apparatus of the present invention issimple to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only,with reference to the following drawings, in which:

FIG. 1 is a schematic, partially cross sectional, side view of part of aportable apparatus in accordance with the present invention, in a startposition;

FIG. 2 is a schematic, partially cross-sectional, side view of theapparatus of FIG. 1 in an end position;

FIG. 3 is a schematic, partially cross-sectional, side view of a part ofan alternative embodiment of a portable apparatus in according with thepresent invention, in a start position;

FIG. 4 is a schematic, partially cross-sectional, side view of theapparatus of FIG. 3 in an end position; and

FIG. 5 is a schematic, partially cross-sectional side view of a secondembodiment of a portable apparatus in accordance with the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 show part of a portable apparatus for calculatingrespiratory oxygen consumption 2 comprising a housing 4, a plunger 6, anoxygen sensor 8 and a movement sensor provided by a first switch 10 anda second switch 12. The apparatus 2 further comprises electroniccalculation means 14.

The plunger 6 is slidably movable inside the housing 4, the interior ofthe housing 4 and the plunger 6 having the same cross-sectional shape.The relative dimensions of the periphery of the plunger 6 and theinterior of the housing 4 being arranged such that there is asubstantially fluid tight fit between the periphery of the plunger 6 andthe interior of the housing 4.

The housing 4 comprises a fluid inlet 16 and a fluid outlet 18.

The oxygen sensor 8 is embedded in the end 20 of the plunger 6. Theoxygen sensor is electrically connected to the electrical calculationmeans 14 by wire 22.

The first switch 10 of the movement sensor is embedded in a side of theplunger 4. The second switch 12 of the movement sensor is embedded inthe interior wall of the housing 4. A wire 24 connects the first switch10 with the electrical calculation means 14 and a wire 26 connects thesecond switch 12 with the electrical calculation means 14.

In use of the apparatus 2, the plunger 6 is arranged in the housing 4 atthe start position as shown in FIG. 1. An exhaled breath is guided intothe fluid inlet 16 of the housing 4. The end of the housing 4 providingthe fluid inlet 16 may act as a mouthpiece for the apparatus 2.Alternatively, a separate mouthpiece (not shown) may be directly orindirectly connected to the housing 4.

The exhaled breath causes the plunger 6 to move away from the fluidinlet 16. The plunger 6 will continue to move in this direction untilthe end 20 of the plunger 6 passes the fluid outlet 18 to reach the endposition as shown in FIG. 2. Thereafter, excess exhaled breath will passout of the fluid outlet 18 and movement of the plunger 6 will cease.

Whilst the plunger 6 is moving from the start position to the endposition, the oxygen sensor 8 is measuring the fraction of oxygen in theexhaled breath. The oxygen sensor 8 sends information of the measurementto the electrical calculation means 14 in the form of an electricalsignal by means of wire 22.

During movement of the plunger 6 from the start position to the endposition, the switches 10, 12 of the movement sensor measure the timetaken to move this set distance. This time is a measurement of the timetaken to exhale a known volume of breath. The switches 10, 12 send themeasurement to the electrical calculation means 14 using wires 24 and26.

The electrical calculation means 14 is programmed to calculate theoxygen consumption of the subject in accordance with Formula I set outabove. In order to make this calculation the operator will need toinsert details for the fraction of oxygen in the inhaled gas. This maybe the standard value for the oxygen content of air, in this case, thisinformation may be previously programmed into the electrical calculationmeans 14. If the oxygen fraction in the inhaled air is measured, themeasured value will need to be input into the electrical calculationmeans 14 before the calculation can be made.

The method and calculation outlined above may be repeated one or moretimes, and the results may be integrated to provide an average value forthe oxygen consumption.

The portable apparatus 2 is of a size and configuration such that it canbe held and carried in the hand by an individual and connected to theelectrical calculation means when desired.

FIGS. 3 and 4 show part of an alternative portable apparatus forcalculating respiratory oxygen consumption 50, comprising a housing 52and a plunger 54.

The housing 52 comprises an opening 56 to allow ingress of external air.The opening 56 is covered by a one way valve 58, which valve 58 allowsingress through opening 56 of air but prevents egress of air throughopening 56.

The housing 52 further comprises a fluid inlet 60 which allows inhaledexternal air to pass from the opening 56 to the subject (not shown)using the apparatus. The fluid inlet 60 also allows exhaled breath topass into the housing 52.

The housing 52 also comprises a gas outlet 62, which allows exhaledbreath to pass out of the housing 62. The gas outlet 62 is connected toa gas collection box 64 by means of a flexible tube 66.

The apparatus 50 further comprises an oxygen sensor 68, located in thecollection box 64, and a movement sensor provided by first and secondswitches 70, 72. The first switch 70 is embedded in the plunger 54. Thesecond switch 72 is embedded in the wall of the housing 52, downstreamof the gas outlet 62.

The oxygen sensor 68 and the switches 70, 72 are connected to acalculation means (not shown) by wires 74.

In use of the apparatus 50, the plunger 54 is arranged in the housing 52at the start position as shown in FIG. 3.

A subject inhales external air through the opening 56 and the fluidinlet 60. The subject then exhales breath into the housing 52 via thefluid inlet 60.

The exhaled breath causes the plunger 54 to move away from the fluidinlet 60. The plunger 54 will continue to move in this direction untilthe end 76 of the plunger 54 passes the gas outlet 62 to reach the endposition shown in FIG. 4. Thereafter, excess exhaled breath will passout of the outlet 62 and into the collection box 64, and movement of theplunger 54 will cease.

During movement of the plunger 54 from the start position to the endposition the switches 70, 72 measure the time taken to move this setdistance. The measurement is sent to the calculation means (not shown)along wires 74.

The oxygen sensor 68 measures the oxygen content of the exhaled breathin the collection box 64, and sends the measurement to the calculationmeans (not shown) by means of wires 74.

The calculation means calculates the oxygen consumption in accordancewith formula I set out above. The calculation is made in the same way asdescribed above in relation to FIGS. 1 and 2.

We refer now to FIG. 5. FIG. 5 shows part of a portable apparatus forcalculating respiratory oxygen consumption (2) comprising a housing(77), a rotor (80) comprising a rotor hub (82) from which extend eightrotor blades (84), an oxygen sensor (78) and a movement sensor providedby a first switch (86) mounted in the housing (77). The apparatus (2)further comprises electronic calculation means (14). The rotor (80) ismounted such that the rotor hub extends horizontally and perpendicularto the longitudinal direction of the housing (77). The rotor (80) isoriented such that the rotor blades (84) operably cooperate with thefirst switch (86) when the rotor rotates within the housing. Thus, eachof the eight rotor blades (84) will sequentially operably cooperate withthe first switch (86) as the rotor (80) rotates.

The housing (77) comprises a fluid inlet (82) and two fluid outlets inthe form of vents (84). The fluid inlet is located at one end of thehousing (77), with the vents (84) located at the other end thereof. Theoxygen sensor (78) is embedded at the end of the housing (77) in whichthe vents (84) are located, downstream of the fluid inlet (82). Theoxygen sensor (78) is electrically connected to electrical calculationmeans (14) by wires (79).

The first switch (86) is located in the housing (77), adjacent to therotor (80), such that as the rotor rotates, the rotor blades (84) arearranged to move past the first switch (86) to thereby operablycooperate with the first switch (86). A wire (88) connects the firstswitch (86) to the electrical calculation means (14).

Use of the apparatus (2) of FIG. 5 will now be described. An exhaledbreath is guided into the fluid inlet (82) of the housing (77). The endof the housing (77) providing the fluid inlet (82) may act as amouthpiece for the apparatus (2). Alternatively, a separate mouthpiece(not shown) may be directly or indirectly connected to the housing (77).The exhaled breath causes the rotor (80) to rotate about the rotor hub(82), thereby causing rotational movement of the eight rotor blades (84)around the rotor hub (82). Whilst the rotor (80) is rotating, the oxygensensor (78) measures the fraction of oxygen in the exhaled breathpassing over the rotor blades (84) and to the oxygen sensor (78). Theoxygen sensor (78) sends information of the measurement to theelectrical calculation means (14) in the form of an electrical signal bymeans of wires (79).

During movement of the rotor (80), the first switch (86) measures thetime taken between adjacent rotor blades (84) passing over the firstswitch (86) of the movement sensor. The first switch (86) also recordsinformation as to the total number of rotor blades (84) which pass thefirst switch (86) during an exhaled breath. The time taken betweenadjacent rotor blades (84) passing the first switch (86), and the totalnumber of rotor blades (84) passing the first switch (86) is ameasurement of the time taken to exhale a known volume of breath. Thefirst switch (86) sends the measurement to the electrical calculationmeans (14) through the wire (88).

The electrical calculation means (14) is programmed to calculate theoxygen consumption of the subject in accordance with Formula I set outabove. The calculation is made in the same way as described above inrelation to FIGS. 1 and 2.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings), may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extend to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. A portable apparatus for calculating respiratory oxygen consumptioncomprising: a housing having a fluid inlet; a flow sensor mounted withinthe housing comprising a movable member movable by air pressure effectedthereupon, and a movement sensor associated with the movable memberwherein the movement sensor comprises one or more sensor switches; anoxygen sensor; and means for calculating the respiratory oxygenconsumption using data obtained from the oxygen sensor and the flowsensor.
 2. A portable apparatus according to claim 1, which is anindirect calorimeter.
 3. A portable apparatus according to claim 1,wherein movement of the movable member within this housing is effectedby passing a fluid into the housing through the fluid inlet.
 4. Aportable apparatus according to claim 3, wherein the fluid is exhaledbreath.
 5. A portable apparatus according to claim 1, wherein the oxygensensor is mounted to the housing.
 6. A portable apparatus according toclaim 1, wherein the oxygen sensor is attached to an end of the movablemember.
 7. A portable apparatus according to claim 1, wherein the oxygensensor is separate from the movable member.
 8. A portable apparatusaccording to claim 1, wherein the movement sensor is arranged to measurethe speed of movement of the movable member.
 9. A portable apparatusaccording to claim 1, wherein a first switch is located on the movablemember and a second switch is located on the housing.
 10. A portableapparatus according to claim 1, wherein the movable member moves betweena start position and an end position during use.
 11. A portableapparatus according to claim 1, further comprising a fluid outlet.
 12. Aportable apparatus according to claim 11, wherein the fluid inlet isprovided by an end of the housing.
 13. A portable apparatus according toclaim 1, wherein the movable member is a plunger slidably mounted withinthe housing, and wherein a fluid outlet is adjacent the end position ofthe plunger.
 14. A portable apparatus according to claim 1, furthercomprising a collection chamber.
 15. A portable apparatus according toclaim 14, wherein the collection chamber is in fluid flow communicationwith a fluid outlet.
 16. A portable apparatus according to claim 14,wherein the oxygen sensor is located in the collection chamber.
 17. Aportable apparatus according to claim 1, further comprising a mouthpieceassociated with the fluid inlet.
 18. A portable apparatus according toclaim 1, wherein an opening in the housing allows external fluid to beinhaled through the apparatus by a subject using the apparatus.
 19. Aportable apparatus according to claim 1, wherein the movable member is aplunger slidably mounted within the housing, and wherein an opening inthe housing that allows external fluid to be inhaled through theapparatus by the subject using the apparatus is located between thefluid inlet and the end of the plunger when the plunger is located in astart position.
 20. A portable apparatus according to claim 18, furthercomprising a one-way-valve to seal the opening.
 21. A portable apparatusaccording to claim 1, wherein the means for calculating the respiratoryoxygen consumption comprises a computer or other electrical device. 22.A method of calculating respiratory oxygen consumption comprising thefollowing steps: (a) passing an exhaled breath into a housing; (b)measuring the fraction of oxygen in the exhaled breath using an oxygensensor; (c) measuring the time taken to exhale the breath using a flowsensor mounted within the housing; and (d) calculating the respiratoryoxygen consumption using the data obtained in (b) and (c), wherein thecalculation of respiratory oxygen consumption is carried out using thefollowing formula:VO ₂ =K×(F _(i) O ₂ −F _(e) O ₂)×V×(30/t)×C  Formula I Where, VO₂ is therespiratory oxygen consumption of the subject, F_(i)O₂ is the fractionof inhaled oxygen, F_(e)O₂ is the fraction of exhaled oxygen, V is thevolume of the exhaled breath over which the measurements are taken, t isthe time taken to exhale the known volume of breath, C is the constantcalorific value for oxygen, and K is a constant allowing forcalibration.
 23. A method as claimed in claim 22, wherein the flowsensor comprises a movable member associated with a movement sensor andstep (a) comprises passing an exhaled breath into a housing to causemovement of the movable member.
 24. A method according to claim 22,wherein step (a) comprises passing an exhaled breath of known volumeinto the housing.
 25. A method according claim 22, wherein the method iscarried out on a portable apparatus comprising: a portable apparatus forcalculating respiratory oxygen consumption comprising; a housing havinga fluid inlet; a flow sensor mounted within the housing; an oxygensensors; and means for calculating the respiratory oxygen consumptionusing data obtained from the oxygen sensor and the flow sensor.
 26. Amethod according claim 22, wherein steps (a) to (d) are repeated one ormore times to obtain an average calculation of oxygen consumption.